A major concern in the transfusion of donated, stored whole human blood or the various blood cells or protein fractions isolated from whole blood is the possibility of viral contamination. Of particular concern are the blood-borne viruses that cause hepatitis and acquired immune deficiency syndrome (AIDS). While any number of cell washing protocols may reduce the viral contamination load for samples of blood cells, by physical elution of the much smaller virus particles, such washing alone is insufficient to reduce viral contamination to safe levels. In fact, some viruses are believed to be cell-associated, and unlikely to be removed by extensive washing and centrifugal pelleting of the cells. Current theory suggests that safe levels will ultimately require at least a 6 log (6 orders of magnitude) demonstrated reduction in infectious viral titer for cellular blood components. This 6 log threshold may be greater for plasma protein components, especially the clotting factors (Factor VIII, Factor IX) that are administered throughout the life of some hemophilia patients.
Viral inactivation by stringent steam sterilization is not acceptable since this also destroys the functional components of the blood, particularly the blood cells and plasma proteins. Dry heat sterilization, like wet steam, is harmful to blood cells and blood proteins at the levels needed to reduce viral infectivity. Use of stabilizing agents such as carbohydrates does not provide sufficient protection to the delicate blood cells and proteins from the general effects of exposure to high temperature and pressure.
Methods that are currently employed with purified plasma protein fractions, often followed by lyophilization of the protein preparation, include treatment with organic solvents and heat or extraction with detergents to disrupt the lipid coat of membrane enveloped viruses. Lyophilization (freeze-drying) alone has not proven sufficient to inactivate viruses, or to render blood proteins sufficiently stable to the effects of heat sterilization. The organic solvent or detergent methods employed with purified blood proteins cannot be used with blood cells as these chemicals destroy the lipid membrane that surrounds the cells. In addition, the safety of existing commercial preparations of such treated plasma protein components may be in question, since many hemophilia patients who routinely receive injections of clotting protein fractions subsequently develop hepatitis.
Another viral inactivation approach first demonstrated in 1958 has involved the use of a chemical compound, beta-propiolactone, with ultraviolet (U.V.) irradiation. This method has not found acceptance in the United States due to concern over the toxicity of beta-propiolactone in the amounts used to achieve some demonstrable viral inactivation.
It is therefore a desideratum to devise an effective viral inactivation treatment for human blood components, which will not damage the valuable blood cells or proteins. The treatment must be selective for viruses, while allowing the intermingled blood cells or proteins to survive unharmed. The treatment must also be nontoxic (i.e., any added chemicals must be used in amounts that will not cause toxicity upon subsequent injection).
While the present invention is concerned with viral inactivation, it is understood that the same concepts and uses disclosed herein can also apply to inactivation of blood-borne bacterial contaminants, or to blood-borne parasitic contaminants. All such infectious organisms rely on nucleic acids for their growth and propagation. Since purified blood plasma protein fractions are substantially free of human nucleic acids, and mature human peripheral blood cells, particularly red blood cells and platelets lack their own DNA, the use of nucleic acid-binding sensitizers is especially useful for the problem of treating blood contaminants.